1. Field of the Invention
The present invention relates to automatic transmissions, in particular for passenger cars, comprising planetary gearsets controlled by hydraulically actuated friction elements such as clutches and brakes, and generally coupled to a start-up coupling device subject to slip, such as a hydraulic torque converter or a fluid coupling.
2. Description of the Prior Art
Most transmissions of this type now on the market offer four gears, and utilize a hydraulic torque converter, two simple planetary gearsets or a Ravigneaux gearset, five friction elements, and a one-way clutch to facilitate first/second and second/first power-on gearshifts. Very often, the torque converter includes a lock-up clutch to eliminate slippage outside transient conditions, so as to improve fuel economy.
Furthermore, a large number of such transmissions also utilize a second one-way clutch to facilitate second/third and third/second, or third/fourth and fourth/third power-on gearshifts and an additional friction element mounted in series with this one-way clutch to release it in other gears. Beside the planetary gearsets, the torque converter and possibly the lock-up clutch, these transmissions thus nowadays utilize a regular number of shift elements comprising five friction elements and one one-way clutch, or six friction elements and two one-way clutches, to provide four gears.
The object of the present invention is a higher performance transmission, which at once utilizes a more advantageous number of shift elements, i.e. five friction elements and one one-way clutch, or five friction elements and two one-way clutches, to provide five gears, sufficiently compact to be easily substituted for such known four-speed transmissions.